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Unformatted text preview: ≥ 0. We recognize the slope, m = 80. Like any slope, we can interpret this as a rate of
change. In this case, C (x) is the cost in dollars, while x measures the number of PortaBoys
so
∆y
∆C
80
$80
m=
=
= 80 =
=
.
∆x
∆x
1
1 PortaBoy
In other words, the cost is increasing at a rate of $80 per PortaBoy produced. This is often
called the variable cost for this venture.
The next example asks us to ﬁnd a linear function to model a related economic problem.
Example 2.1.6. The local retailer in Example 2.1.5 has determined that the number of PortaBoy
game systems sold in a week, x, is related to the price of each system, p, in dollars. When the
price was $220, 20 game systems were sold in a week. When the systems went on sale the following
week, 40 systems were sold at $190 a piece.
1. Find a linear function which ﬁts this data. Use the weekly sales, x, as the independent
variable and the price p, as the dependent variable.
2. Find a suitable applied domain.
3. Interpret the slope...
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